1. Field of the Invention
The present invention relates to an image display apparatus and an image display method in which light sources are driven to emit light for displaying an image, and relates to an image display apparatus and an image display method in which light sources emitting light to a displaying unit are controlled to display an image on the displaying unit.
2. Description of Related Art
A liquid crystal display makes a liquid crystal panel pass or block light emitted from a backlight, to display an image. The color reproducibility, color contrast and electric power consumption of liquid crystal display apparatus are mainly depend on the performance or control of a liquid crystal panel and backlight. Recently, it is proposed to utilize a driving method (referred as to “area active driving method”, hereinafter) in which a backlight is divided into plural areas and a luminous efficiency of each area is controlled.
When a displayed image includes a low intensity portion, the area active driving method decreases the luminous efficiency of a backlight area corresponding to the low intensity portion and sets the passing rate of liquid crystal panel based on the decreased luminous efficiency. The luminous efficiency of the backlight can be optimized for each area, as described above. Thus, it is possible to reduce the electric power consumption required for whole of the backlight. In addition, the decrease of luminous efficiency for each area can reduce so-called “too little black phenomenon” (e.g., a condition where black looks faintly luminous on the screen turned off just now), and improve the contrast and image quality.
The area active driving method can utilize a RGB-LED (light-emitting diode) light source, as the backlight, configured with three LEDs dedicated to red (R), green (G) and blue (B). In order to utilize this RGB-LED light source, it is required not only to adjust the luminous efficiency for each area but also to control respective three LEDs in each area. For example, when a displayed image corresponding to some area is configured with only blue, the LED dedicated to red (referred as to “R-LED”, hereinafter) and the LED dedicated to green (referred as to “G-LED”, hereinafter) are turned off, the LED dedicated to blue (referred as to “B-LED”, hereinafter) is turned on, and the passing rate of liquid crystal display panel is set in accordance with the luminous efficiency of B-LED. Thus, it is possible to display the image that is configured with only blue and has the high color purity. As described above, it is possible to control only the required LED among the LEDs located in each area. Thus, the utilization of RGB-LED light source can reduce the electric power consumption larger than the utilization of white light source. Furthermore, it is possible to obtain the high color gamut of displayed image, because the color purities of respective primary colors can be kept high.
A patent document 1 describes an apparatus and method that utilize such an area active driving method described above and can control the luminance and color property of local area on the backlight. In the apparatus and method of patent document 1, the liquid crystal display panel is divided into plural areas, and the backlight is configured with LEDs where light are emitted to each area from plural LEDs. The luminous efficiency of LED is controlled in accordance with the peak gradient value of each area on the liquid crystal display panel.    Patent document 1: Japanese Patent Application Laid-Open No. 2005-338857